1. Field of the Invention
The present invention generally relates to optical transmission circuit devices and, more particularly, to an optical transmission circuit device having a board on which electronic devices are mounted to as to perform data transmission between boards.
2. Description of the Related Art
In recent years, the Internet has become popular rapidly which enables almost all the information services and transactions being achieved on the Internet. Accordingly, the importance of the Internet as a civil infrastructure has been increasing. With such development in the Internet, there is a demand for improvements in an operation speed, expandability and operating rate in a server system that supports the Internet.
A blade server such as shown in FIG. 1 has a cabinet 101 in which a plurality of unit devices 102 are stored in a stacked state. Each unit device 102 shown in FIG. 2 is provided with many boards 103. Each board 103 is provided with a CPU (Central Processing Unit), a memory circuit, a hard disk apparatus, etc. Each board 103 constitutes one independent system. Such a blade server is capable of dealing with an increase in the number of transactions by increasing the number of boards 103 and increasing the number of the unit devices 102. Additionally, the blade server has an advantageous function to replace the malfunctioning board 103 while operating the blade server.
In the conventional unit device, data transmission between boards is performed through electric cables connected by dizzy chain on a backside of a back plane to which the boards are connected. However, in a high-speed electric signal transmission such as, for example, an electric signal transmission in a GHz order, a signal waveform is blunted and a signal voltage is suppressed, which results in weakness in noise, and it becomes difficult to perform a high-quality signal transmission. In order to solve such a problem, Japanese Laid-Open Patent Application No. 2001-102765 suggests an optical transmission method using optical fibers.
By the way, it is possible to set the transmission rate per one channel to a GHz order in the optical transmission method. However, when connection is made by optical fibers 104 on the side of the back plane 108 of the unit device 102 shown in FIG. 2, it is difficult to connect by many optical fibers 104 since it is difficult to increase a density of connection parts 105 such as connectors provided on the back plane 108. Therefore, it is difficult to connect the boards according to parallel transmission. Further, since it is difficult to bend the optical fiber 104 to have a small radius of curvature, there is a problem in that there is less freedom in design of the connection parts 105.
Moreover, there may be a problem in that an operation error and thermal destruction may occur due to heat generated by a CPU and memory circuits that are mounted to the boards 103 with high density. For this reason, cooling fans 106 are provided on the backside of the back plane to which the boards are fixed and a front side of the boards 103 so that a cooling air caused by the cooling fans flows from a front side of the unit device 102 to the backside so as to cool the CPU and memory circuits. In such a unit apparatus 102, since the cooling air hardly flows upper and lower portions and side portions of the apparatus, a ventilation holes are 109 are provided on the back plane 108 to which the boards 103 are connected as shown in FIG. 2 so as to acquire passages of the cooing air. Accordingly, an area of the back plane 108 used for signal transmission is limited, and it is difficult to reserve an area of the connection parts 105 for connecting the boards 103 by many optical fibers.